It has long been the practice to arrange string, cord, or line (hereafter referred to as string) across the loop formed by the racquet frame to provide a light, resilient surface (hereafter referred to as the strung surface) to hit balls or other objects with power and control. It is common to arrange the string, usually kept in tension, in a criss-cross weaved fashion across the racquet frame. The string is commonly supported directly by the racquet frame, or supported by flexible grommets, or a grommet strip mounted on the outside periphery of the racquet frame. The plurality of strings thus arranged forms the racquet's strung hitting surface.
Almost all tennis, squash, badminton, and racquetball racquets use hitting surfaces of string that is arranged in some manner across the loop formed by the racquet frame.
Racquet designers and manufacturers construct racquets with good playing characteristics. High string resiliency is often thought to improve a racquet's performance. Hence, much effort has been expended to provide strong resilient strings to achieve or improve high racquet performance. It is also common practice to vary stiffness of a racquet frame to control and improve a racquet's performance characteristics. Racquet stiffness can be controlled by the racquet manufacturer with the choice of racquet construction material, or by the internal or external configuration of the racquet, or by a combination of these techniques. Other approaches to improve a racquet's performance include the use of extra weights on parts of the racquet frame, or forming the racquet frame to a shape different than the common oval shape, or making the racquet frame larger for a large string surface, or supporting the strings on radially compliant springs or material, or a combination of these techniques.
The common approaches for improving a racquet's performance have drawbacks. For example, racquet power (the amount of energy imported to a hit ball) can be improved by increasing racquet stiffness. Unfortunately, high stiffness makes it more difficult to control direction of a hit ball, makes it more difficult to impart spin to a ball, and may cause a racquet to vibrate when hitting the ball especially with off-center hits. In another example, attempts to increase size of the `sweet spot` (the region of high and most even rebound response) by making the area of the strung hitting surface larger, such as by increasing the size of the racquet frame loop or by attaching extra weights to the top or sides of the racquet frame, may be ineffective. Theory and experiments indicate that relatively little may be gained by these measures, while several draw-backs may appear. For example, a racquet's rotary inertia about its longitudinal axis (the line along the racquet's handle) may be increased, or the racquet may become top-heavy, thus reducing the quickness (maximum racquet head acceleration obtainable by a given player) and maneuverability of the racquet, which in turn detrimentally affects the racquet's overall power and control. In another embodiment, all of part of the racquet's strings may be supported on radially compliant springs or radially compliant material. This may gain some racquet performance benefits because the ball's dwell time of the racquet is increased, but these benefits are degraded by accompanying friction losses caused by strings moving radially across their cross-strings.